This study examines the use of individual development plans (IDPs) in a structured mentoring program as an effective mechanism for reducing identity-related anxiety for underrepresented trainees and increasing their learner agency. Social cognitive theory served to provide the theoretical framework for our implementation of IDPs and our investigation of the effects of completing IDPs on trainees attaining academic goals and subsequent success in enrolling in competitive PhD programs. Results suggest that IDPs are also an effective tool that can allow faculty mentors to provide the social support necessary for trainees to persist in accomplishing their short- and long-term learning goals. Additionally, trainee self-agency, in the use of the IDP and mentoring, seemed to provide an alternative narrative to ability as a sole predictor of STEM achievement. We also found that IDPs helped foster social support networks, providing stability, predictability, and a sense of belonging. Specifically, IDPs helped foster the emotional and informational support necessary for trainees to persist, despite obstacles, as they strived to attain their learning goals.